Transducer plate for electro-acoustic transducers

ABSTRACT

The invention relates to a transducer plate for electro-acoustic transducers, such as used in telecommunications technology, having a carrier plate and a ceramic plate arranged on a carrier plate. The invention teaches a transducer plate which is dimensioned so that it can be used in a microphone, a receiver or a piezoelectric VF ringing device despite the different voltage response factors required for each application. The following dimensions should preferably be used: transducer plate diameter (0 2 )=43 mm; ceramic plate diameter (0 1 )=30 mm; transducer plate thickness (d)=150 microns; and ceramic plate thickness (1)=90 microns.

BACKGROUND OF THE INVENTION

The invention relates to a transducer plate for electro-acoustictransducers, which utilizes a piezoelectric ceramic coating.

Existing transducer plates are disclosed by German patent No. 1,961,217and by the following published German patent applications: No.3,107,344, No. 3,107,293, No. 3,007,834, No. 3,005,708 and No.3,007,808. These references disclose a transducer element which isclamped between bearing bodies.

Piezoelectric transducers belong to the category of reversibletransducers, which can emit sound when electrically excited or produceelectricity when excited by sound energy. Accordingly, these transducerscan be used in many applications, such as microphones, earphones or VFringing devices in telephone systems. Depending upon the use, thetransducer must be specially adapted to the requirements of thatapplication. In some circumstances it is necessary to provide anamplifier, while in other applications resonator cavities and soundguidance channels must be specially matched to the particular type oftransducer being used.

To be economical it is desirable to utilize the least number ofcomponents for the various types of transducer applications.

SUMMARY OF THE INVENTION

The object of the invention is to provide a transducer plate which canbe used for various telecommunication functions so that the cost of thetransducer and the total number of transducers that must be maintainedas replacements is reduced.

In general, the invention features a transducer plate, provided with apiezoelectric ceramic coating, for electro-acoustic transducers, inwhich the diameter of the transducer plate is between 40 and 45 mm, thediameter of the ceramic is between 25 and 35 mm, the thickness of thetransducer plate is between 100 and 250 microns, and the thickness ofthe ceramic is between 50 and 150 microns.

In preferred embodiments the transducer plate has a diameter

substantially equal to 43 mm; the ceramic has a diameter

substantially equal to 30 mm; the transducer plate has a thickness

substantially equal to 150 microns; the ceramic has a thickness

substantially equal to 90 microns; the thickness of the ceramic isapproximately 100 microns and dielectric constant of the ceramic isgreater than or equal to 3000.

Other features and advantages of the invention will be apparent from thefollowing detailed description, and from the claims.

For a full understanding of the present invention, reference should nowbe made to the following detailed description and to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in detail with reference to thefollowing drawings:

FIG. 1 is a cross-section of a transducer plate.

FIG. 2 is a plan view of the transducer plate shown in FIG. 1.

DETAILED DESCRIPTION

Transducer plate 4, shown in in the FIGS. 1 and 2, consists of carrierplate 1, composed of an aluminum alloy or brass, and piezo-ceramic plate3, which is connected to carrier plate 1 at interface 5, by adhesivelayer 2. The adhesive layer can consist of a relatively thick layerwhich is distributed over the entire surface of the carrier plate. Inthe following embodiment, however, adhesive layer 2 consists of arelatively thin coating which is only applied beneath the ceramic plateand which possesses a negligible thickness.

The following dimensions are for a transducer element formed inaccordance with the invention:

    ______________________________________                                        Diameter of piezoelectric                                                                        .0..sub.1 = 25-35 mm                                       plate 3                                                                       Diameter of carrier                                                                              .0..sub.2 = 40-45 mm                                       plate 1                                                                       Thickness of ceramic                                                                             1 = 50-150 microns                                         plate 3                                                                       Thickness of carrier                                                                             d = 100-250 microns                                        plate 1                                                                       ______________________________________                                    

The dimension restrictions are determined by the high voltage responsefactor required for sound transmitters, by the ability to process theplates to certain thicknesses and diameters, and by the frequencyresponse characteristics. Therefore, the thickness of both the ceramicand the transducer plate cannot fall below a minimum value. In addition,upper dimension limits also exist. The maximum diameter of the ceramicis determined by the manufacturing limitations imposed by the facilitywhich produces the thin ceramic plates. The diameter of the carrierplate is only limited by the maximum possible capsule diameter.

When the transducer is utilized as a receiver in a telephone atransducer capacitance of at least 200 nF is necessary to attain therequisite voltage response factor so that the receiver is matched to thetelephone circuit. This can be achieved by using a very thin ceramicplate and an average dielectric constant.

However, to use the same transducer element for other applications inaccordance with the object of the invention, it is desirable to selectan average ceramic thickness of approximately 100 microns and adielectric constant for the ceramic of greater than or equal to 3000.This allows the transducer to be used for all applications.

Therefore, the present invention teaches a single transducer plate whichcan be used successfully in a microphone, a receiver and for a VFringing device, despite the different voltage response factors requiredfor each application.

There has thus been shown and described a novel apparatus for atransducer plate for electro-acoustic transducers which fulfills all theobjects and advantages sought. Many changes, modifications, variationsand other uses and applications of the subject invention will, however,become apparent to those skilled in the art after considering thisspecification and the accompanying drawings which disclose embodimentsthereof. All such changes, modifications, variations and other uses andapplications which do not depart from the spirit and scope of theinvention are deemed to be covered by the invention which is limitedonly by the claims which follow.

What is claimed is:
 1. In a transducer plate for electro-acoustictransducers for telephone apparatus formed by a piezoelectric ceramiclayer provided with electrodes on both sides and connected with asupport plate, the improvement wherein the transducer plate required fora microphone, a receiver or tone ringer has a transducer plate diameterbetween 40 and 45 mm, a ceramic diameter between 25 and 35 mm, atransducer plate thickness between 100 and 250 microns, and a ceramicthickness between 50 and 150 microns.
 2. The improvement of claim 1,wherein the transducer plate has a diameter substantially equal to 43mm.
 3. The improvement of claim 1, wherein the ceramic has a diametersubstantially equal to 30 mm.
 4. The improvement of claim 1, wherein thetransducer plate has a thickness substantially equal to 150 microns. 5.The improvement of claim 1, wherein the ceramic has a thicknesssubstantially equal to 90 microns.
 6. The improvement of claim 1,wherein the thickness of the ceramic is approximately 100 microns andthe dielectric constant of the ceramic is greater than or equal to 3000.